[Proposal] Improve Contributor Ladder and Role Definitions

[jpower432]

Objective

Currently, our governance describes a flat maintainer structure. We need to formalize how contributors advance and define the maintainer split between the subprojects.

Proposed Ladder

• Sustained Contributor: Active community member submitting PRs/Issues.
• Subproject Maintainer: PR approval and write access for a specific repository or collection of repositories.
• Core Maintainer: Organization-wide oversight, spec maintainers, and binding votes on project governance.
• Community Manager: Neutral facilitator for outreach and moderation and documentation maintenance.

Proposed Completion Criteria

• Define the specific expectations and "rung" requirements for each role in the ladder and the process to move to the "rung".
• Amend the existing Governance doc to distinguish between "Core" and "Subproject" maintainer roles.
• Standardize how we list people across repos so their role is clear (Can we just stick to security-insights?)
• Create GitHub Team Mapping and Implementation
• Implement CODEOWNERS to automatically request reviews from the correct Subproject team.
• Reflect the new contributor ladder on the website's Community page.

[jpower432]

cc @eddie-knight